Method of removing airlines in a cathode ray tube



Se t. 26, 1967 H. E. REXFORD 3,343,934v

METHOD OF REMOVING AIRLINES IN A CATHODE RAY TUBE ori inal Filed Feb. 15, 1961 1NVENTOR. Harry E. Rexford ATTORNEY United States Patent 3,343,934 METHGD OF REMOVING AIRLINES IN A CATHODE RAY TUBE Harry E. Rexford, Bel Air, Md., assignor to Corning glass Works, Corning, N.Y., a corporation of New -ork Continuation of abandoned application Ser. No. 89,386, Feb. 15, 1961. This application May 10, 1965, Ser. No. 454,354

3 Claims. (Cl. 6555) This application is a continuation of application Ser. No. 89,386, filed Feb. 15, 1961, now abandoned.

This invention relates to television picture tubes and more particularly to the improvement of electrical and strength characteristics of television picture tube envelope necks through the elimination of airlines ordinarily therein.

In the manufacture of glass television picture tube envelopes the neck portion, which houses the electron gun, is generally formed from drawn tubing. Such necks, comprised of sections of conventionally drawn tubing, have very thin longitudinal gas pockets, cells or inclusions, herein called airlines, which contain a small amount of entrapped gas and/ or vapor, herein called gas. When such television picture tube envelopes are subjected to high voltages, thin glass Wall regions of the neck, which separate said airlines from the neck bore, crack releasing the entrapped gas in said airlines, together with particles of glass chipped off by the escaping gas, into the tube interior. The released gas tends to destroy the vacuum integrity, while the glass particles interfere with the electron gun operation rendering the costly tube useless.

Many present television tubes utilize voltages ranging from 5,000 to 25,000 volts. In addition, durnig manufacturing, the nearly completed bulb is subjected to a spotknocking process utilizing voltages up to 50,000 volts and sometimes higher. (Spot-knocking is an electrical cleaning process.) It has been found that the use of such voltages creates an electrical field of suflicient strength to ionize the airline gases, causing the glass walls separating the airlines from the neck interior to crack or burst, through increased pressure, temperature or change of other conditions of the gas. Furthermore, the presence of these airlines causes a change in the dielectric strength of the neck. Present considerations of higher operating voltages, with resultant higher spot-knocking voltages, will cause the problem to become more acute.

These airlines are most troublesome when they are close to the interior surface of the neck, that is, within the inner third of the wall thickness, and also when their gas pressure is low, since there is correspondingly less glass strength to contain the gas as the airlines are located closer to the inside surface and the gas is more readily ionized at lower pressures.

Heretofore, various methods have been employed to reduce the effects of airlines for electrical and strength purposes. Such methods resulted in changing the direction of the airlines, or causing them to transform into bubbles, and the like, while some applications require the use of different and more costly materials.

The term drawing is used herein only as it is understood in the art of glass tube manufacture. By this term is meant tubing formed by the downdraw method such as, for example, that taught by E. Danner, Patent No. 1,218,598, or L. Sanchez-Vello, Patent Nos. 2,009,- 326 and 2,009,793; or tubing formed by the updraw method. These methods are described in Glass Engineering Handbook by E. B. Shand, Second edition, McGraw-Hill Book Co., Inc., 1958, Library of Congress Catalog Card Number 58-10006.

By the term redrawing is meant tubing formed by reheating conventionally drawn tubing as defined hereinice above, which tubing was drawn to a larger size than ultimately required, and then pulling the heated tubing over a mandrel thereby reworking the glass and reducing the tubing size.

In accordance with this invention a television picture tube neck can be produced without airlines while using present materials, by employing a conventionally drawn tube having a wall thickness and diameter larger than required and subsequently heating and reworking such tube by redrawing over a mandrel or otherwise changing the structure of the glass to the desired wall thickness and diameter, which reworking causes said airlines to collapse and/ or Work themselves out to the surface. The resulting tube is therefore free from airlines, that is, airlines have been removed therefrom, and possesses much improved dielectric characteristics.

A specific object of this invention is to provide an improved television picture tube, the neck of which is free from airlines.

Another object is to provide an improved television picture tube having more uniform dielectric characteristics in the glass neck portion.

Still another object is to provide a method for the elimination of airlines in television picture tube necks.

Additional objects, features and advantages of the present invention will become apparent, to those skilled in the art, from the following detailed description and the attached drawing on which, by way of example, only the preferred embodiment of this invention is illustrated.

FIG. 1 is an elevation of a fragment of a conventional television picture tube illustrating the airlines present in the neck portion.

FIG. 2 represents a tube drawn to oversized dimensions in the conventional manner, with airlines present therein, preparatory to the removal of said airlines.

FIG. 3 is a sectional view of the tube represented in FIG. 2 being redrawn over a mandrel to proper dimensions, while airlines therein are being collapsed and worked out of the glass.

FIG. 4 is an elevation of a fragment of the improved television picture tube.

FIG. 1 illustrates typical airlines 10, shown in exaggerated size, which are generally found within the walls of the tube neck 12, of a conventional television picture tube 14. Said airlines, containing gases composed primarily of air, result from gases entrapped in the molten supply body of glass in the form of bubbles, which bubbles are elongated to form airlines in the course of conventional drawing of tubing. The tube neck 12 houses the electron gun, not shown, to which gun high voltages are applied during manufacture and use of the tube. These high voltages develop an electrical field of sufiicient strength to ionize the gases within airlines 10, causing the gas pressure and temperature to increase, which in turn causes the glass between the airlines and the inside surface of the neck to crack and break out, releasing the entrapped gas and allowing glass particles to interfere with the electron gun operation.

Tubing 16, shown in FIG. 2, having been drawn by conventional methods to a much larger diameter and greater wall thickness than required for a television picture tube neck, in accordance with this invention, illustrates the presence of airlines 18, inherently occurring in conventionally drawn tubing. As shown in FIG. 3, the airlines 18, are removed through reworking tubing 16, by redrawing it over a mandrel 20, while said tubing is heated by means of electric heating element 22, during which reworking said airlines are collapsed and/ or work themselves out to the surface, assisted by a subatmospheric pressure maintained within cavity 24, of tubing 16, during the redrawing process. This reworking results in properly sized, airline free tubing 26.

FIG. 4 illustrates a television picture tube 28, produced in accordance with this invention, where neck 30 is free from airlines.

A typical example of carrying out this invention may be illustrated by the following example: Glass tubing, of appropriate composition, is drawn to approximately two times the diameter and wall thickness required for a television picture tube neck. This tubing is then suitably reheated and redrawn over a mandrel to the required size, while a vacuum source is connected to the cavity of the oversized tubing. In the course of this reworking, the airlines collapse or are worked out to the surface. A thus separately formed television picture tube neck composed of the reworked tubing may then be assembled with the remainder of the television picture tube envelope components, namely the face plate and funnel, in a conventional manner, such as, for example, by fusing the neck to the end of the tube funnel.

Tests conducted with neck tubing of this type showed superior electrical qualities and more uniform dielectric properties, without glass chipping into its interior, While the vacuum integrity of the tubing itself Was maintained.

It is obvious that airlines may be removed and a glass having improved electrical characteristics can be produced for any application Where glass is used in connection with electrical elements. Although the present invention has been described with respect to specific details of certain embodiments thereof, it is not intended that such details be limitations upon the scope of the invention eX- cept insofar as set forth in the following claims.

I claim:

1. A method of manufacturing a television picture tube envelope having in combination a face plate, a funnel, and a separately formed neck comprising the steps of drawing glass tubing having a size larger than that of said neck, reheating and redrawing said tubing to collapse and remove all airlines therefrom, and thereafter fusing the airline free tubing to said funnel to form the neck of said picture tube.

2. A method of manufacturing a television picture tube envelope having in combination a face plate, a funnel, and a separately formed neck comprising the steps of drawing glass tubing having a wall thickness and diameter larger than that of said neck, reheating and redrawing said tubing over a mandrel to collapse and remove all airlines therefrom, and thereafter fusing the airline free tubing to said funnel to form the neck of said picture tube.

3. The method of claim 2 further comprising the step of reducing the pressure Within the drawn tubing while it is being redrawn over said mandrel.

References Cited UNITED STATES PATENTS 1,737,662 12/1929 Loepsinger l09 2,699,014 1/1955 Van Steenis 65-55 2,886,920 5/1959 Breadner et al 65292 X DONALL H. SYLVESTER, Primary Examiner.

A. D. KELLOGG, Assistant Examiner. 

1. A METHOD OF MANUFACTURING A TELEVISION PICTURE TUBE ENVELOPE HAVING IN COMBINATION A FACE PLATE, A FUNNEL, AND A SEPARATELY FORMED NECK COMPRISING THE STEPS OF DRAWING GLASS TUBING HAVING SIZE LARGER THAN THAT OF SAID NECK, REHEATING AND REDRAWING SAID TUBING TO COLLAPSE AND REMOVE ALL AIRLINES THERERFROM, AND THEREAFTER FUSING THE AIRLINE FREE TUBING TO SAID FUNNEL TO FORM THE NECK OF SAID PICTURE TUBE. 